The present invention is directed to a process for the manufacture of flexible molded parts from urethane and urea group containing elastomers through reaction in closed molds of i) an A-component containing isocyanate reactive materials and inorganic fillers with ii) a B-component that consists essentially of isocyanate-terminated semi prepolymers. The A-component contains both inorganic fillers and additives with acidic groups which enables easier working in of the components. The components are mixed and reacted using reaction injection molding technology.
The manufacture of polyurethane/urea elastomers through reaction of reactive mixtures produced by reaction injection molding from isocyanate-terminated semi-prepolymers and mixtures of aromatic diamines and higher molecular weight amino and hydroxyl group-containing compounds is, for example, known from U.S. Pat. No. 5,262,448 (corresponding to German Offenlegungschrift 3,914,718). The process permits the manufacture of elastomers with better mechanical characteristics in comparison to products which were manufactured based on the one shot process (such as is described in U.S. Pat. No. 4,218,543, which corresponds to German Auslegungschrift 2,622,951). A disadvantage of the molded parts manufactured based on the semi-prepolymer process is in the greater shrinkage (volume reduction after mold release). The use of molding tools which were provided for the one shot process led to molded parts with reduced volume when using these same tools for the semi-prepolymer process, such that the application of the semi-prepolymer process would require the construction of new molding tools which would better fit the circumstances.
Another problem is the frequently desired, additional use of inorganic filler and reinforcing materials of known type. Thus, for example, short fiber glass fillers could be suspended in the large volume B-component (NCO-semi prepolymer), but little use is made of this possibility due to the residual moisture contained in these fillers that reacts with NCO-groups. It is also known, for example, that certain film-forming agents or fiberglass containing adhesion promoters, and Wollastonite, cannot be worked in at all on the isocyanate side (B-component).
The A-component, consisting primarily of amine chain extending agents, shows on the other hand a bad cohesion capability for inorganic fillers so that the working of the A-component containing such fillers is almost impossible even under agitation.